Microparticles and small particles may be formed using existing jet milling techniques. Such systems, like the Micron-Master™ operated by Jet Pulverizer Co. of Moorestown, N.J. are capable of making friable or certain crystalline materials into small particles using impact methods. Most conventional jet mills operate by injecting fluidized particles into a grinding chamber. The particles are picked up and accelerated, entrained and bombarded against themselves by jets of expanding compressed air or gases entering tangentially to the chamber. Particles are classified to a very narrow particle size distribution by action of centrifugal forces on the particles and drag forces of the gas leaving the mill.
Organic, inorganic and engineered compounds and materials typically fall into three primary categories: (1) friable and crystalline; (2) technically brittle, but extremely tough; and (3) pliable or resilient (which covers many polymeric and elastomeric materials). Friable or crystalline materials can usually be ground with typical jet or mechanical technologies. Tough materials often cannot be ground satisfactorily due to energy limitations that existing impact technologies can apply to these particles. Particle reduction of pliable and resilient materials, like plastics and elastomers, has been limited to mechanical technologies with average particle sizes ranging from about 50-500 microns, with results being dependent on the glass transition temperature (Tg) of the material and the ability to make some materials brittle and finer using the help of cryogenics using liquid nitrogen.